An American university student who had been held prisoner in North Korea for 17 months died at a Cincinnati hospital on Monday, just days after he was released from captivity in a coma, his parent said.

Otto Warmbier, 22, who was arrested in North Korea while visiting as a tourist, had been described by doctors caring for him last week as having extensive brain damage that left him in a state of "unresponsive wakefulness."

"Unfortunately, the awful torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible beyond the sad one we experienced today," the family said in a statement after Warmbier's death at 2:20 p.m. EDT (1820 GMT).

His family has said that Warmbier lapsed into a coma in March 2016, shortly after he was sentenced to 15 years of hard labour in North Korea.

Physicians at the University of Cincinnati Medical Center, where he died, said last Thursday that Warmbier showed no sign of understanding language or awareness of his surroundings, and had made no "purposeful movements or behaviours," though he was breathing on his own.

There was no immediate word from Warmbier's family on the cause of his death.

The circumstances of his detention in North Korea and what medical treatment he may have received there remained a mystery, but relatives have said his condition suggested that he had been physically abused by his captors.

The University of Virginia student and Ohio native was arrested, according to North Korean media, for trying to steal an item bearing a propaganda slogan.

North Korea released Warmbier last week and said he was being freed "on humanitarian grounds."

The North Korean mission to the United Nations was not available for comment on Monday.

U.S. President Donald Trump issued a statement offering condolences to the Warmbier family and denouncing "the brutality of the North Korean regime as we mourn its latest victim."

The president drew criticism in May when he said he would be "honoured" to meet with North Korean leader Kim Jong Un.

"If it would be appropriate for me to meet with him, I would absolutely, I would be honoured to do it," Trump said in the interview. "If it's under the, again, under the right circumstances. But I would do that."

The student's father, Fred Warmbier, said last week that his son had been "brutalized and terrorized by the Pyongyang government and that the family disbelieved North Korea's story that his son had fallen into a coma after contracting botulism and being given a sleeping pill.

Doctors who examined Otto Warmbier after his release said there was no sign of botulism in his system.

Warmbier was freed after the U.S. State Department's special envoy on North Korea, Joseph Yun, travelled to Pyongyang and demanded the student's release on humanitarian grounds, capping a flurry of secret diplomatic contacts, a U.S. official said last week.

Tensions between the United States and North Korea have been heightened by dozens of North Korean missile launches and two nuclear bomb tests since the beginning of last year. Pyongyang has also vowed to develop a nuclear-tipped intercontinental ballistic missile capable of hitting the U.S. mainland.

Secretary of State Rex Tillerson said the United States holds North Korea accountable for Warmbier's "unjust imprisonment" and demanded the release of three other U.S. citizens still held by Pyongyang - Korean-Americans Tony Kim, Kim Dong Chul and Kim Hak Song.

Jonathan Bae, whose father, Korean-American missionary Kenneth Bae spent two years in North Korean captivity before his release in 2014, expressed sadness at Warmbier's death.

"My heart goes out to the family. I will pray for them and hope they find peace," Jonathan Bae said.

Young Pioneer Tours, the group with which Warmbier travelled to North Korea, will no longer be organising tours for U.S. citizens to the isolated country, Troy Collings, a company director, said in a statement.